The Balmer jump in astrophysical hydrogen plasmas

It is shown that, according to accepted theoretical concepts, there should be no intensity jump at the edge of the Balmer continuum, nor at that of other hydrogen series. We point out three reasons for a fairly smooth increase of the intensity to occur at the continuum edge. As a result, the jump sometimes spreads over hundreds of ångstroms, due mainly to the electron density inhomogeneity of solar plasma. Furthermore, the Doppler and Stark effects also give rise to a considerable spread of the series edge. We point out that excess continuum emission over a relatively narrow spectral interval before the continuum edge can result from overlapping of line wings.     

Spectrophotometry of bright Be stars

We present new measurements of the distribution of energy in the continuum for eight Be stars in the optical region (3200-7600 Å). The effective temperatures of these stars have been estimated from their observed fluxes. It is found that, in general, pole-on stars show near-infrared excess emission. It is interesting to note that the Balmer jumps for stars having an infrared excess are systematically smaller than for those lacking the infrared excess.Variability of ultraviolet and infrared excess emissions in these stars has been discussed. The stars 59 Cyg, 66 Cyg, 28 CMa, and 27 CMa show large variations in their continuum at ultraviolet (UV) and infrared (IR) regions.     

Distribution of absolute energy of bright Be stars in pleiades

We present newly measured energy distributions from 3200–7500 Å of five late-type Be stars in Pleiades cluster for search of peculiarities of Be stars continuum energy distributions. Empirical effective temperatures of Be stars have been derived by comparing observed and computed fluxes in the visible region. The variation of the flux in the Balmer continuum region of Pleione (28 Tau) has been discussed.     

Observations of the infrared triplet of singly ionized calcium

Observations are presented of the Caii infrared triplet (8498 Å, 8542 Å, and 8662 Å) at three positions on the solar disk to make possible direct analyses of the lines and comparisons with theoretical computations. The source functions for the two strongest lines (8542 Å and 8662 Å) are equal at those heights corresponding to the wings of the lines (¦¦ > 0.4 Å) but not to those of the cores. We suggest that the apparent source function inequality in the cores is due to limb darkening caused by inhomogeneities in the chromosphere.Of the National Bureau of Standards and University of Colorado.     

The determination of physical parameters for circumstellar clouds

The possibility of the detection of circumstellar clouds around hot stars have been shown based on the analysis of observed equivalent widths of resonance line 2852 Mgi of interstellar origin. An attempt has been made to combine two methods, earlier suggested — Method of Doublet 2800 Mgii and Method of Depression — for the determination of the parameters of circumstellar clouds. The sequence of the determination of these parameters is illustrated on the application of this combined method for circumstellar clouds around five hot stars. The value of the mean absorption coefficientk ₀ for the system of resonance lines in the region of depression 2400 Å, is obtained. An application of the conception of spectral classification of circumstellar clouds has been realized.     

Observations of resonance polarization in Cai λ4227

The resonance polarization in Ca i 4226.73 has been measured close to the solar limb for three values of = cos. The polarization has maxima in the wings at about –500 and + 400 mÅ from the line center, the plane of polarization (electric vector) being parallel to the solar limb. The blue wing is more polarized than the red wing, contrary to earlier results of Brückner (1963). Local minima in the polarization curves occur at the position of blends. The polarization in the wings increases rapidly with decreasing . At = 0.15 the maximum polarization in the blue wing is about 2.4%.The observations are in good qualitative agreement with the recent theory of Dumont et al. (1973), but the observed polarization degrees are significantly smaller than the computed values. This may be explained by the inadequate formula for van der Waals broadening used in the theoretical calculations. Much of the discrepancies between observed and computed values disappear if the recent value of Lites (1974) for the collisional damping constant is used. Further improvements in theory and observation are discussed.     

New C13N14 search regions in the solar spectrum

Ten new rotational line positions, due to the (0,0) red C¹³N¹⁴ band, are calculated to fall squarely within continuum regions 1–2 Å wide in the near infrared solar spectrum, , 10 990–11 630. Precision observations of the isotopic line strengths in this spectral region, albeit difficult, should resolve the present ambiguity in the blue-violet observations of whether or not the solar C¹²/C¹³ ratio is equal to or larger than the terrestrial ratio.     

The Balmer 9 and Balmer 11 lines of He ii in the Sun

We identify the Balmer 9 and 11 lines of He ii at 959 Å and 942 Å in solar spectra. These lines are produced mainly by recombination following photoionization of He ii by coronal XUV radiation. From analysis of the line intensities, we confirm the theoretical model of Avrett et al. (1976), who found that an appreciable amount of He⁺⁺ is present at temperatures of 1–2 × 10⁴ K and that the anomalously strong He ii 304 line is produced primarily by collisional excitation. We also confirm the suggestion of Kohl (1977) that the photoionization-recombination process is more important in active regions than in the quiet Sun, and we find that the 304 line is produced largely by recombination in solar flares.     

Spectrophotometric observations and evolutionary status of ten Be stars

The continuum energy distribution data of ten Be stars — namely, HR 1761, HR 1786, HR 1820, Ori, Ori, OT Gem, Lyr, HR 7983, Cyg, and 59 Cyg — have been presented in the wavelength range 3200–8000 Å. The observed energy distribution curve shows near infrared excess for majority of Be stars and a double Balmer jump for HR 8047 and HR 8146. Empirical effective temperatures of these stars have been estimated by comparing the observed continuum energy distributions with that of computed theoretical models given by Kurucz (1979).On the basis of an HR diagram with evolutionary tracks for different solar masses the masses of these Be stars have been estimated. Position of these studied stars on the HR diagram suggests that these Be stars may be in the stage of core contraction after exhausting hydrogen at the centre and have undergone hydrogen exhaustion in the thick shell.     

The He i 10 830 Å chromosphere and filament associated structures

Full disk, He I 10 830 Å solar spectroheliograms have been generated using the Haleakala Stokes polarimeter-spectrometer. The spectroheliograms, with spatial resolution of 10 × 16 arc sec and wavelength bandpass of 0.53 Å, were developed for the detection of coronal holes, and have been compared with nearly simultaneous H and Ca K flltergrams.Areas of reduced helium absorption have been noted in the neighborhood of filaments and neutral zones in the longitudinal solar magnetic field. The existence of these helium lanes is discussed in terms of their relationship to H filament channels or to the coronal cavities which surround prominences.     

The high-dispersion continuous ultraviolet solar spectrum and the Balmer-jump

Among the intensities, determined at about 200 wavelengths between 3000 and 4100 Å in the spectrum of the centre of the sun's disk (Houtgast, 1965), the 32 highest ones (windows) were plotted and compared with absolute intensities given by other authors.The intensities in between the Fraunhofer lines from 3600 to 4000 Å, as determined here for the first time with high dispersion, reveal a detailed picture of several absorption features, one of which can be attributed to a Balmer jump of 0.03, a value in accordance with that found for stars and in agreement with the strengths of the high Balmer lines.The much higher value of the Balmer jump for the sun, as quoted in literature, in reality refers to the total intensity jump between 4000 and 3600 Å, which is mainly due to the crowding of Fraunhofer lines.     

The transfer of polarized radiation in spectral lines: Solar-type stellar atmospheres

The polarization structure in several spectral lines in solar type stars is computed using the method described by McKenna (1981, 1984a). The frequency redistribution function used for these calculations is a linear combination ofR _II andR _III. The line profiles and polarization structures have been computed for several weak solar resonance lines includingKi 7664 Å, Sri 4607 Å, Baii 4554 Å, for various polar angles along the stellar disk. Both the line profiles and polarization structures as well as the center to limb behavior of the line center polarization agree well with observations.The somewhat stronger resonance line Cai 4227 Å shows a different polarization structure when compared to the weaker solar resonance lines. It is found that for strong resonance lines the proper redistribution function to be used is a linear combination ofR _III andR _v (see McKenna, 1981, 1984b; Heinzel, 1981). The major reason for this is that for strong resonance lines both the upper and lower levels are broadened by collisions. This violates the assumptions upon which the redistribution functionsR _II andR _III are based.     

Flare-related changes in the profiles of six photospheric spectral lines

The profiles of six photospheric absorption spectral lines (Fei 5250 Å, Fei 5324 Å, Fei 5576 Å, Cai 5590 Å, Cai 6103 Å and Fei 6165 Å), measured in the kernel of a 2N solar flare and in a quiet-Sun area, were compared. The observations were carried out with an echelle spectrograph of the Crimean Astrophysical Observatory. It was shown that, compared to the quiet-Sun profiles, the flare profiles are shallower in the line core and are less steep in the wings. Therefore, measurements of the longitudinal magnetic field made with a magnetograph system which uses the Cai 6103 Å  spectral line, can be underestimated by 18–25% in areas of bright H ribbons of a moderate solar flare. Modeling of the solar photosphere performed by using a synthesis method showed that, in a solar flare, the enhanced core emission seems to be related to heating of the photosphere by the flare, whereas the decrease of the slope of the wings was presumably caused by the inhomogeneity of the photospheric magnetic field.     

Fine Structure of the solar atmosphere from near-limb observations in three wavelengths

We analyze a time series of high-resolution observations near the limb, in the continuum, in the Mg b ₁ line (-0.4 Å off line center), and in the wings of H (+0.75 Å). The observations were obtained with a CCD camera at the Vacuum Tower telescope of the Sacramento Peak Observatory. We study the association of facular points, as they appear at different heights of the solar atmosphere (continuum, b ₁ - 0.4 Å, H + 0.75 Å) with the feet of fine dark mottles.     

Moment method for multiple scattering of solar Lα radiation in the nearby interstellar medium

The problem of solar L (1216 Å) photons scattered coherently by interplanetary medium is solved for a realistic density distribution using a simple three-stream division of the radiation field.     

Solar flare X-ray spectra

Spectra of 3 large flares on 24 Oct., 5 Nov. and 16 Nov. 1970 in the region = 1.75–1.95 Å, obtained with the help of the Intercosmos-4 satellite during solar activity maximum are given. The physical conditions at the initial and final (decaying) phases are mainly studied. The line spectra are compared with hard continuum in the region 8–80 keV and results of polarization measurements, obtained simultaneously aboard the same satellite.     

A search for polarization in Ellerman bombs

Ellerman bombs, also called moustaches, are transient brightenings at tiny (< 1 arc sec) points in the lower chromosphere whose spectra are characterized by elongated emission wings on the hydrogen Balmer lines. Babin and Koval recently found linear polarization as high as 20% in bombs, but no physical process that could produce such a high degree of polarization was suggested. A new observational study of polarization in Ellerman bombs is reported here. Images of 32 bombs were obtained with a digital video system viewing the Sun through a 6 Å filter at the Sacramento Peak Vacuum Tower Telescope. A novel polarizing beamsplitter divided each image into two interleaved polarized components which passed simultaneously through a single set of optics and were separated only during data analysis. The sensitivity threshold of the measurements was 1%. In 4 cases out of 32, linear polarization above 2% was detected. The higher incidence of > 2% polarization reported by Babin and Koval is not confirmed.     

Scanner observations of shell stars ϕ Persei and ψ Persei

Spectrophotometric energy distribution data of the shell stars Per and Per are reported in the wavelength range 3200–8000 Å. The effective temperature of these stars is derived by comparison of observed energy distribution with theoretical models. Both the stars show higher values of derived effective temperature. The continuum energy distribution in the ultraviolet region has also be discussed.     

CH Cygni in the transition to its cool phase

U, B, V-observations, supplemented by spectrophotometric measurements of the symbiotic variable CH Cyg in the years 1982 to 1984 show that the star has reached its blue maximum phase of its recent outburst in the first half of 1984. From end of July, 1984 on the object underwent a considerable drop in brightness and an increase of its colour indices, and which indicates that it was on the way to its cool phase. Also the spectroscopic observations show that the blue continuum still observed at the beginning of July, 1984 has disappeared in October–November, 1984 and the strong absorption features, typical for a M-type giant were re-appearing. A remarkable intensity increase of the emission features, especially those of the Balmer lines, took place within this time interval. The rapid flickering variations of CH Cyg had also reached the culmination amplitude in July, 1984. There seem to be three periodicities present in these flickering variations with cycle lengths of 7.7 min, 21 min, and 60 min. Though these observational findings would be consistent with the M-type blue subdwarf component binary model with mass flow from the M6-III giant to the companion, the genuine binary nature of CH Cyg could not be established beyond doubt.     

Solar line blocking for disk-center and disk-averaged radiation from 3300 to 6860 Å

The line blocking is tabulated for 10 Å ( < 6300 Å) or 20 Å ( > 6300 Å) wide intervals. It follows from the spectral averages and the local continuum derived by Neckel and Labs from high-resolution Fourier transform spectra, which had been obtained by J. Brault at Kitt Peak. The internal accuracy (the scatter) is in the order of 0.1%. Significant systematic errors arising from local distortions of the adopted continuum level can be excluded. Larger errors are to be expected only near the Balmer limit, where the localization of the continuum is very ambiguous.